This invention relates to a new use of cationic layered materials, compositions comprising these materials, and a process for the preparation of cationic layered materials.
A Cationic Layered Material (CLM) is a crystalline NH4-Me(II)-TM-O phase with a characteristic X-ray diffraction pattern. In this structure, Me(II) represents a divalent metal and TM stands for a transition metal. The structure of a CLM consists of negatively charged layers of divalent metal octahedral and transition metal tetrahedral with charge-compensating cations sandwiched between these layers.
The CLM structure is related to that of hydrotalcite and hydrotalcite-like materials. These materials, also referred to by the skilled person as layered double hydroxides (LDH) or anionic clays, are built up of Me(II)-Al hydroxide sheets with exchangeable anions in the interlayer. Analogous to the term “anionic clay” being a synonym for hydrotalcites and hydrotalcite-like materials, “cationic clay” can be used as a synonym for CLM.
CLMs are known from the prior art. M. P. Astier et al. (Ann. Chim. Fr.Vol. 12, 1987, pp. 337-343) prepare CLMs by first dissolving ammonium heptamolybdate and nickel nitrate in an aqueous ammonia solution and subsequently altering the pH by evaporating ammonia, resulting in precipitation. After aging, washing, and drying, pure crystalline CLMs are formed with a characteristic X-ray diffraction pattern.
A similar precipitation procedure is disclosed in U.S. Pat. No. 6,156,695 for the preparation of CLMs containing Ni, W, and Mo. D. Levin, S. Soled, and J. Ying (Chem. Mater. Vol. 8, 1996, pp. 836-843; ACS Symp. Ser. Vol. 622, 1996, pp. 237-249; Stud Surf, Sci. Catal. Vol. 118, 1998, pp. 359-367) also disclose the preparation of CLMs. Their process involves the steps of (a) precipitating a divalent metal salt and aluminium nitrate, (b) aging the precipitate to form an anionic clay, (c) calcining the anionic clay to form a mixed oxide, and (d) contacting and reacting the mixed oxide with ammonium heptamolybdate—thereby removing aluminium ions and incorporating molybdate ions—resulting in a CLM with a trace amount, e.g. 0.63 wt %, of aluminium.
It has now been found that CLMs can suitably be used in or as a catalyst or catalyst additive in a hydrocarbon conversion, purification, or synthesis process, particularly in the oil refining industry and Fischer-Tropsch processes. Examples of processes where CLMs can suitably be used are catalytic cracking, hydrogenation, dehydrogenation, hydrocracking, hydroprocessing (hydrodenitrogenation, hydrodesulfurisation, hydrodemetallisation), polymerisation, steam reforming, base-catalyzed reactions, Fischer-Tropsch, and the reduction of SOx and NOx emissions. They are especially suitable for use in FCC processes, particularly as active material in FCC catalysts or catalyst additives for (i) the reduction of the nitrogen and/or sulfur content of fuels like gasoline and/or diesel and/or (ii) the reduction of SOx and/or NOx emissions.
Therefore, the invention relates to the use of a cationic layered material in a hydrocarbon conversion, purification, or synthesis process. This cationic layered material may have been prepared according to the process of the invention described below, or according to any other process, e.g. the prior art processes mentioned above.
The prior art processes for preparing CLMs all use water-soluble divalent metal and aluminium salts as starting material, which is particularly disadvantageous. First of all, these soluble metal salts are relatively expensive. Second, they require a precipitation process, which is not very attractive to perform on an industrial scale, because it involves repeated filtering and washing steps of very fine (colloidal type) particles. This involves large-scale plant equipment, very low throughput capacities, and large volumes of contaminated waste water. Third, the use of salts implies the use of anions. These anions either have to be removed by washing and filtering steps—incurring the above filtration problems with the fine-particled materials and waste water streams containing, e.g., nitrates, sulphates, halogens, etc.—or will be emitted as environmentally harmful gases like nitrogen oxides, halogens, sulphur oxides, etc. during the drying or calcination steps.
The present invention also provides a process for the production of cationic layered materials using inexpensive raw materials. In particular, the use of metal salts is avoided, resulting in a process that is particularly environmentally friendly and more suited to the environmental constraints that are increasingly imposed on commercial operations. Furthermore, this process does not involve a precipitation process. In addition, in one process embodiment there is no necessity of forming an anionic clay as intermediate, thereby simplifying the process.